linux-kernel - Re: [PATCH v3 5/8] x86/sme: Replace occurrences of sme_active() with cc_platform

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Date:   Thu, 23 Sep 2021 00:05:58 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-graphics-maintainer@...are.com,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        Brijesh Singh <brijesh.singh@....com>,
        Joerg Roedel <joro@...tes.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Christoph Hellwig <hch@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v3 5/8] x86/sme: Replace occurrences of sme_active() with
 cc_platform_has()

On Wed, Sep 22, 2021 at 09:52:07PM +0200, Borislav Petkov wrote:
> On Wed, Sep 22, 2021 at 05:30:15PM +0300, Kirill A. Shutemov wrote:
> > Not fine, but waiting to blowup with random build environment change.
> 
> Why is it not fine?
> 
> Are you suspecting that the compiler might generate something else and
> not a rip-relative access?

Yes. We had it before for __supported_pte_mask and other users of
fixup_pointer().

See for instance 4a09f0210c8b ("x86/boot/64/clang: Use fixup_pointer() to
access '__supported_pte_mask'")

Unless we find other way to guarantee RIP-relative access, we must use
fixup_pointer() to access any global variables.

-- 
 Kirill A. Shutemov